This invention relates to a strainer mounted on a hydraulic control unit for an automatic transmission. More particularly, the invention relates to a strainer used upon being mounted in an oil passage of a valve body or casing.
An automatic transmission comprises such components as a torque converter, speed gearing and a hydraulic control unit. When the working oil used in these components becomes contaminated with foreign matter, various hydraulic pressure valves employed in the components develop a valve sticking phenomenon and may become inoperable as a result. This accounts for the majority of the early troubles encountered in automatic transmissions. Various measures in terms of design and manufacture have been taken to remedy this phenomenon since the occurrence of valve sticking adversely affects the image of the vehicle equipped with the transmission. One of these measures which is well-known is to provide a reticulate strainer just ahead of the valve that is likely to stick in the hydraulic control unit. This expedient prevents foreign matter such as chips from flowing past the valve. However, mounting the strainer in the oil passage within the valve body presents problems because of space considerations.
In order to solve the problem of space, a variety of strainers have been proposed in the form of a cylinder or disk for use in the oil passage of a valve body, by way of example. In FIGS. 3 through 7, there is shown an example of a strainer in the form of a cylinder, as disclosed in the specification of Japanese Patent Application Laid-Open (Kokai) No. 59-39317. FIGS. 8 through 11 illustrate an example of a disk-shaped strainer, as disclosed in the specification of Japanese Utility Model Application Laid-Open (Kokai) No. 59-36814.
With reference to FIGS. 3 through 5, the cylindrical strainer, indicated at numeral 31, comprises a frame 32 and a tubular reticulate member 33 fixedly secured thereto. The frame 32 is made of nylon and the tubular reticulate member 33 of tetron. The frame 32 includes an annular portion 35 at one thereof, a disk-shaped portion 36 at the other end thereof, and four circumferentially spaced bar-shaped ribs 37 interconnecting the portions 35, 36. The annular portion 35 has an outer periphery 34 for being fitted into an oil passage. The tubular reticulate member 33 is fixedly imbedded in the frame 32 to completely encircle the ribs 37 and the peripheral interstices therebetween with the exception of the inner side 38 of the annular portion 35 of frame 32. A bar-like projection 39 is formed on the outer surface of the disk-shaped portion 36.
As shown in FIGS. 6 and 7, the strainer 31 is used upon being mounted in a cylindrical space formed in a valve body 40 at the joint 42 between the valve body 40 and a separator plate 41. More specifically, this cylindrical space is formed in a portion of the valve body at which oil passages perpendicularly intersect each other, such as a portion 45 where there is communication between an oil passage groove 43 extending parallel to the joint 42 and an oil passage 44 crossing the joint 42 at right angles. Thus, as shown in FIG. 6, the strainer can be easily mounted at any location where there are a fitting seat portion 46 for receiving the outer periphery of the annular portion of frame 32, and an annulus 47.
The strainer 31 is formed at the joint between the valve body and the separator plate, and use is made of the cylindrical space interconnecting the oil passage groove extending parallel to the joint and the oil passage perpendicular thereto. Acordingly, the strainer 31 can be reduced in size and mounted with ease while providing a large mesh area.
FIGS. 8 and 9 illustrate a strainer 51 in the form of a disk. The strainer 51 comprises a tubular member 52 having a bore 53, and a reticulate member 54 secured within the bore 53. The tubular member 52 consists of tetron and the reticulate member 54 of stainless steel. The tubular member 52 comprises an upper enlarged diameter portion 56 and a lower reduced diameter portion 57 separated from each other by an intermediate step or shoulder 55. A locking pawl 58 is projectingly formed on the outer peripheral part of the reduced diameter portion 57. The end of the large diameter portion 56 of tubular member 52 is formed to include four cut-outs 59 spaced equidistantly in the peripheral direction. Similarly, the end of the reduced diameter portion 57 of tubular member 52 is formed to include four cut-outs 60 spaced equidistantly in the peripheral direction.
The reticulate member 54 is placed so as to cover the mid-portion of the bore 53 of tubular member 52 and has its outer peripheral portion imbedded and secured in the wall of the tubular member 52.
As shown in FIGS. 10 and 11, the strainer 51 is mounted with the shoulder 55 and the locking pawl 58 engaged in an oil passage opening 66 in a separator plate 65 clamped between a valve body 62 and a valve body cover 63. The oil passage opening is of a predetermined diameter sufficient to provide a circulation area for oil required of the reticulate member 54.
Since the strainer 51 is of a reduced axial size and a flow passage is provided by the cut-outs, the strainer 51 can be mounted within a space having a limited axial dimension but at the same time provides a large mesh area.
With the conventional strainer that uses the reticulate member, however, it is difficult to remove all foreign matter, inclusive of contaminants having a very small size. In particular, chips of ferrous material account for a major portion of the contaminants of small size, and needle-like chips of a fairly great length can easily pass through the reticulate member. This means that the strainer by itself is not necessarily sufficient for the purpose of removing the foreign matter contained in the oil. Although it may be contemplated to make use of a permanent magnet in the oil duct to remove magnetic contaminants such as ferrous chips, it is difficult to provide a location for mounting the magnet and the mounting operation is complicated and troublesome.